It is well known in the medical sector, and more specifically in the surgical sector, that it is becoming increasingly important to have tissues available for grafting into living beings to meet the growing need to replace parts of organs or whole organs.
The creation of biological substitutes that are prepared in the laboratory and then transplanted into animal or human recipients is a medical procedure known by the name of “tissue engineering”.
According to a known technique, tissues for grafting are prepared in the laboratory by implanting cells into a matrix consisting of an inorganic supporting medium generally called a “scaffold”.
The “scaffold”, which is used to compensate for a loss of substance of the organ being treated, facilitates the three-dimensional organisation of the cells until the formation of new tissue has been completed.
The scaffold must naturally then undergo a process of degradation until it disappears completely and is replaced by the regenerated tissue, which is facilitated by the cells implanted in said scaffold.
Transplants can be obtained using this method with either artificial or natural scaffolds (i.e. from a “donor”) obtainable from humans or animals, such as the oesophageal wall.
To use a natural scaffold harvested from a donor for transplanting into another human being, the tissue must be treated first to eliminate all the cells existing between the fibres of the connective tissue, and then to reimplant human cells belonging to the intended recipient of the graft (the “host”) in order to avoid rejection phenomena.
The techniques used to create a scaffold, i.e. an acellular matrix, starting from tissues harvested from a donor, are well known and are consequently not described in detail here; briefly, they involve immerging the tissue to be treated in a fluid containing enzymatic substances capable of digesting and destroying the living cells contained within the tissue without damaging the tissue's connective fibres.
After creating an acellular tissue matrix, ready to receive the cells obtained from the host, said tissue, or scaffold, is prepared in a so-called “Petri dish” (or similar container), which is a tray commonly used in biological laboratories, on the bottom of which the tissue to revitalise is rested.
The tissue is revitalised by implanting stem cells from the future recipient and nourishing them with a cell culture broth that feeds the cells, keeping them alive and enabling them to multiply and become disseminated.
Basically, the stem cells initially placed on the upper surface of the tissue move through the natural interstitia in the tissue of the scaffold—interstitia that were previously occupied by the donor's cells.
After a given period of time, under controlled temperatures and in the presence of the nutritional substances contained in the culture broth, the living cells reposition themselves in the interstitia of the tissue, which is then ready for transplantation into the host organ.
It should be noted that the cells generally used to revitalise the scaffold are stem cells, which subsequently become differentiated (or may have already done so) and acquire the specific function of the organ in which the revitalised tissue is grafted.
The success or failure of the transplantation of the tissue treated in this way depends on a capillary diffusion of the cells through the tissue matrix.
If this diffusion proves difficult or occurs on the surface, but not in depth, the transplanted tissue is not adequately revitalised and a necrotic process begins, leading to the failure of the transplant.
From the above considerations, it is clear that it is essential and important, not to say indispensable to success, to ensure the in-depth revitalisation of every part of the tissue, particularly through its full thickness.
For the time being, even when the preparatory and revitalising treatments are applied for a sufficiently lengthy period of time, it is still impossible to ensure results reliable enough to guarantee against any graft failures.
This is due to the scarce penetration of the living cells being reimplanted in the scaffold.
In practical terms, this drawback considerably restricts the opportunity to prepare tissues suitable for transplantation because thicker tissues are not fully revitalised after the transplant since they cannot be penetrated in sufficient depth.
It is consequently evident that the current technique is only suitable for the transplantation of tissues of very limited thickness, e.g. not exceeding approximately 0.1 mm.
U.S. Pat. No. 5,112,354 discloses the preparation of a bone allograft wherein first all soft tissue is removed and then the surface is textured to produce a pattern of holes adapted to facilitate the demineralization of the bone and to increase the surface for interaction with subsequently introduced mesenchymal cells. The holes are produced by laser or mechanical drilling.